4. Disperse systems Flashcards
What is a suspension?
solid in a liquid
What makes up a dispersion?
- a dispersed phase
- a continuous/dispersing phase
What is an emulsion?
liquid in a liquid
What is an aerosol?
solid or liquid in air
What is a coarse dispersion?
- solute not dissolved and is visible
- suspensions
- emulsions
What is a fine dispersion?
- solute not completely dissolved
- magmas and gels
what are colloidal dispersions?
- solute not completely dissolved BUT not visible
- will scatter light
What are molecular solutions?
- solute completely dissolved in solvent
- true solutions won’t scatter light
Why are disperse systems thermodynamically unstable systems?
- larger particles have a greater tendency to separate from the dispersing phase
- solids settle, liquids rise to top
- must restore uniform distribution while moderate agitation for proper dosing
What are the advantages of suspensions?
- ease of swallowing
- flexibility of dose
- bad tastes can be masked
- drug may have increased stability
What are the disadvantages to suspensions?
- physically unstable, will separate over time
- if you don’t shake, dosing will be wrong
- pt may not like mouth-feel (esp. if particle size if large)
What are the desirable attributes of a suspension?
- should settle slowly and be re-dispersed with gentle shaking
- particle size should remain fairly constant with shelf life
- should pour readily and evenly
What are the parameters of sedimentation rate?
- it’s a function of particle size
- inverse function of viscosity (more viscous = slower settling)
- small particle sizes can cake or agglomerate (stick together)
- floccules can prevent caking
What are floccules?
a loose aggregation of particles
Why are floccules good?
- they form higher sediment volumes than non-flocculated suspensions
- loose structure = easy to re-disperse
How can you form floccules in suspension?
by adding surfactant or sometimes electrolytes
- at specific concentrations they may neutralize surface charges
Why should a viscosity increasing agent be adding to suspensions with floccules?
What kind of viscosity agent should be used?
- since the particles size is bigger (floccules), you need a higher viscosity to reduce settling
Want an agent that is:
- higher viscosity at low shear rates (storage, after shaking, pouring)
- low viscosity at high shear rates (shaking)
Infants and neonates should have minimal exposure to:
- preservatives
- alcohol
- propylene glycol
What is the expiration date for aqueous extemporaneous solutions?
14 days in the refrigerator
- to prevent microbial growth and increase stability
- need to add preservatives if need for longer than 14 days
What are the constituents of suspensions or structured vehicles?
- active ingredient
- wetting agent
- suspending agent
- flocculating agent
- protective colloid
- sweetener
- preservative
- buffer system
- color agent
- flavor agent
- antifoaming agent
What type of emulsion is more occlusive?
w/o
What type of emulsion has better drug release?
o/w
What is creaming?
In emulsions, when internal-phase droplets:
- rise to the top (o/w)
- sink to bottom (w/o)
How can you stabilize an emulsion?
- surfactants
- hydrocolloids
- solid particles
What do surfactants do?
- reduces repellent forces between phases
- reduces attractive forces within each phase
- breaks globules into smaller droplets
Can be:
anionic - sodium docusate, sodium oleate
non-ionin - spans and tweens
cationic - halides
What do hydrocolloids stabilize emulsions?
- provide protective multi-molecule layers around dispersed droplets
- provide charge, droplets repel each other
- may swell to increase viscosity
How do solid particles stabilize an emulsion?
- form layer around droplet and swell
- this increases viscosity and reduces attraction
What is HLB?
What is it used for?
Hydrophilic-lipophilic balance
System designed to aid in determining the amount and type of emulsifier needed to produce stable emulsions
What are the 3 methods of extemporaneous compounding?
- continental
- english
- beaker
- bottle
What is the continental method?
- primary emulsion of oil, water and emulsifier (4:2:1)
- acacia used as gum emulsifier
- gum and oil mixed, then all of water added with vigorous trituration
What is the english method?
- 4:2:1
- gum mixed with water to make mucilage
- oil added in parts with vigorous mixing
What is the bottle method?
- works best with low viscosity oil
- 4:2:1
- gum and oil added to bottle - mix vigorously
- then water, mix vigorously
- make an in situ soap
What is the beaker method?
- only 5% of synthetic emulsifier is needed
- water soluble materials dissolved in water
- oil soluble materials dissolved in oil
- both solutions heating to 70 in water baths
- internal phase added to external phase and mix until cooled to room temp
Describe hydrophilic colloidal dispersions.
- like water, hydrate and swell to increase viscosity
- may carry a charge, the charge keeps particles separated
- quite stable with affinity between particles and continuous phase
Describe hydrophobic colloidal dispersions.
- less stable than hydrophilic (no interaction between colloid and continuous phase)
- stabilize by developing attraction between colloid particles and continuous phase
- can carry a charge, repulsive forces and brownian motion keeps colloids dispersed
- addition of electrolyte may neutralize charge and cause settling
What is a two-phase gel?
gel made with discrete particles
What is a single-phase gel?
if large organic macromolecules are uniformly distributed with no apparent boundaries between the dispersed and continuous phase
What type of auxillary label should be used on disperse systems?
- shake well
- refrigerate (if applicable)
- external (if applicable)
Why are disperse systems packaged in oversized containers?
- to facilitate shaking
What is the usual concentration of surfactants in disperse systems?
2-5%
ex. tween 80, span 20
What will happen to a disperse system if a preservative is not used?
- will only last 2 weeks with refrigeration
What is the ingredient function of:
- hydrochlorothiazide
- methycellulose
- citric acid
- sodium benzoate
- aspartame
- orange flavor
- purified water
- API
- suspending agent
- pH adjuster
- preservative
- sweetener
- flavor
- vehicle
